This invention relates generally to rotary piston engines and in particular to rotary piston engines that include first- and second-piston assemblies that are interconnected for alternate variable-speed rotation whereby pistons of the slower piston assembly comprise trailing pistons during the power and intake phases of the engine operating cycle.
The only currently commercially available rotary engine, the Wankel engine, is compact and lightweight, simple in design, capable of producing high torque output, and easy to maintain. It is not energy efficient, however, because the sealing attached to apexes of the piston cannot completely seal off the cavity on the chamber wall used for the spark plug, so gas leaks between subchambers every time the apex of the piston passes the spark plug cavity. In the so-called cat-and-mouse types of rotary engines such as those found in U.S. Pat. No. 5,133,317xe2x80x94Sakita; U.S. Pat. No. 4,901,694xe2x80x94Sakita; U.S. Pat. No. 4,646,694xe2x80x94Fawcett; U.S. Pat. No. 3,398,643xe2x80x94Schudt; U.S. Pat. No. 3,396,632xe2x80x94LeBlanc; U.S. Pat. No. 3,256,866xe2x80x94Bauer; U.S. Pat. No. 2,804,059xe2x80x94Honjyo; U.S. Pat. No. 5,433,179xe2x80x94Wittry; and the present invention, the severity of possible gas leaks caused by the spark plug cavity on the working chamber wall should be much less because the pistons are wide enough to cover the cavity, and the piston rings on either side of piston seal off the spark plug cavity from the subchambers. The only way to completely eliminate gas leaks, however, is to eliminate the spark plug cavity on the wall, or embed the spark plug in the piston and make it easily accessible from the outside. Installing a spark plug within the piston should have the further advantage of permitting ignition timing to be optimally adjusted to the speed of rotation or richness of the gas mixture independently of the piston location.
The present invention is an extension of the work presented in U.S. Pat. No. 5,381,766 by the present inventor, Sakita. In said patent, the present inventor described a rotary engine equipped with a gear mechanism that enables intermittent rotation of pistons, namely, the stopping of the trailing pistons while the leading pistons are rotating at maximum speed. The gear mechanism provides said engine with the smallest overall working chamber and the thinnest piston to produce a specified output. There is a possibility, however, that some applications, including the aforementioned spark plug adoption or adoption in diesel engines in which robust structures are required, may require thicker pistons than are possible in engines with intermittent rotation of pistons. Also, at high-speed operation, engines with intermittent operation may not necessarily be the most efficient; this is because the nonstopping piston of the intermittent operation engine rotates faster than the faster piston in the nonintermittent rotation engine, and may cause higher mechanical loss. Thus, the present inventor felt the need to devise a gear set that allows rotation of the pistons for any designed speed profiles.
Two sets of gear geometries are considered: one set belongs to the same family of gear geometries disclosed in U.S. Pat. No. 5,381,766 by Sakita, and another set belongs to a family of gear geometries disclosed in U.S. Pat. Nos. 4,003,681 and 4,028,019 by Wildhaber.
The earlier patent (U.S. Pat. No. 5,381,766xe2x80x94Sakita) uses spur gears of varying radius or gears with roller bearings for the heart- and teardrop-shaped gears. If the spur gears are used and teeth are fully attached around the periphery of the gear, the teeth may have to be small and the gears undesirably wide. Larger teeth may be used if gear teeth are not attached in the vicinity of the teardrop-shaped gear""s apex and the corresponding sections of the heart-shaped gear; not attaching gear teeth at a portion of the heart- and teardrop-shaped gears, however, would require the gears to be twice as thick. This is another area for improvement the present invention addresses.
Another improvement focused on in the present invention is the adoption of technologies that are known to further improve engine output and energy efficiency with no or little additional power requirements, such as the use of different compression ratios for compression and expansion (U.S. Pat. No. 5,433,179xe2x80x94Wittry) and the use of an air nozzle for scavenging exhaust air (NACA Report No.469, Increasing the Air Charge and Scavenging the Clearance Volume of a Compression-Ignition Engine, J. S. Spanogle, C. W. Hicks, and H. H. Foster, Langley Field, Va., June 1933).
With the present invention, realization of rotary piston engines that produce the highest output and are the most energy efficient for given design conditions will become possible.
An object of this invention is the provision of a working chamber that is equipped with a means to allow easy access to spark plugs installed inside the piston assembly.
An object of this invention is the provision of interconnecting piston assemblies to enable variable-speed operation of the pistons as specified by the engine designer.
An object of this invention is the provision of a pair of gears that remain engaged at all times while rotating with specified rotational speed profiles.
An object of this invention is the provision of a working chamber such that the compression ratio computed as the maximum volume of the compression subchamber over the minimum volume of the compression subchamber is in an acceptable range for a given engine type but will be higher if the compression ratio is computed as the maximum volume of the combustion subchamber over the minimum volume of the combustion subchamber, wherein the minimum volume of the compression subchamber equals the minimum volume of combustion subchamber.
An object of this invention is the provision of a working chamber equipped with an exhaust port wider than the piston width to permit ending of the expansion phase before the piston reaches the end of the combustion phase.
An object of this invention is the provision of an air nozzle that is installed at the mouth of the exhaust port to scavenge the exhaust air that remains within the exhaust subchamber at the end of the cycle.
An object of this invention is the provision of a pair of gears that are equipped with teeth specially designed for gears with variable rotational speeds.
The present invention includes an engine with working chamber within which the first and second piston assemblies rotate about a rotational axis. Each piston assembly includes a hollow piston hub to which one or more pairs of diametrically opposed pistons are attached. The pairs of pistons divide the working chamber into a plurality of subchambers in which a single pair of diametrically opposed pistons per piston assembly provides four subchambers in the working chamber, and two pairs of diametrically opposed pistons per piston assembly provide eight subchambers in the working chamber. A spark plug having electrodes with spark gaps is installed within the piston assembly such that the electrodes communicate with a subchamber through a hole bored at the center of the piston surface. A spark plug maintenance hole is bored on the side of the engine housing for accessing the spark plug from outside. The first and second piston assemblies are connected to the first and second input shafts, respectively, of the differential means for rotation in the same direction. With one complete revolution of the piston assemblies, four engine operating cycles are completed for a four-piston engine and eight operating cycles are completed for an eight-piston engine, with each operating cycle comprising the power, exhaust, intake, and compression phases. The interconnection between the first and second piston assemblies results in rotation of each piston such that as the leading piston increases its rotational speed, the trailing piston decreases its rotational speed, and as the leading piston decreases its rotational speed, the trailing piston increases its rotational speed. The engine""s working chamber includes a compression subchamber that is smaller than the combustion subchamber. The intake port, exhaust port, and piston widths are adjusted so that the compression ratio computed as the maximum volume over the minimum volume of the compression subchamber will be within the normally acceptable range for a given engine type, but the compression ratio computed as the maximum volume over the minimum volume of the combustion subchamber is generally higher than the normal compression ratio.
The present invention includes differential means having first and second input shafts and an output shaft, together with first and second noncircular gear sets. Each of the first and second gear sets includes two types of intermeshing noncircular gears we call Sakita type 1 and type 2 gears (or type 1 and type 2 gears). The extension of the differential output becomes the output shaft, which is connected through a circular gear set to an idler shaft to which type 2 gears are affixed. The type 1 gears of the first and second gear sets are connected to the first and second differential input shafts, respectively. The type 1 gears rotate with widely varying speeds, while the type 2 gears rotate at the same rate as the output shaft of the engine. The differential assures that the sum of the rotational speeds of the type 1 gears equals twice the rotational speed of the type 2 gears.
In the alternative embodiment disclosed and claimed in the present application, each of the first and second gear sets includes gears which we call the Wildhaber-Sakita type 1 and type 2 gears (or to avoid confusion, simply the type 3 and type 4 gears, respectively). The extension of the differential output becomes the output shaft, which is connected through a circular gear set to an idler shaft to which type 4 gears are affixed. The type 3 gears of the first and second gear sets are connected to the first and second differential input shafts, respectively. The type 3 gears rotate with widely varying speeds, while the type 4 gears rotate at twice the rate of the output shaft of the engine. The differential assures that the sum of the rotational speeds of the type 3 gears equals the rotational speed of the type 4 gears.